The invention relates to a controller for a commutator motor operated with the aid of a phase-gating controller, having a steady and also a jerky rotational behavior of the commutator motor, for which purpose the phase-gating controller is assigned a first and a second control device, for a first and a second gating of the half waves of an AC voltage.
The speed of commutator motors can be controlled in a variable fashion by the assignment of an electronic system. Such an electronic system can, for example, include a phase-gating controller in the case of AC operation, or a pulse-width modulator in the case of DC operation. Such controllable commutator motors are also advantageously applied in the case of electric hand tools.
There are applications for electric hand tools, for example in the case of power-intensive screwing operations and reliable drilling into sheet metal and aluminum, in the case of which it is advantageous when the electric tool is provided with an electronic system with the aid of which it is possible to achieve a rising and falling torque or a pulsed speed in the case of a commutator motor.
Such an electronic system is disclosed, for example, in DE 195 01 430 A1. A description is given there of a method for driving an electric motor which is applied in the case of electric tools. An electric voltage (U) is applied to the electric motor (1) with variable pulses (11, 11xe2x80x2, 20) in such a way that the rotor of the electric motor is moved at a settable speed (n1, n2). Phase-gating controllers or pulse-width modulators are applied for this purpose. The jerky or impulsive movement of the rotor of the electric motor (1) is achieved by virtue of the fact that parts of individual pulses (11, 11xe2x80x2, 20) are cut out by superimposing a pulse pause (12, 12xe2x80x2, 22) with a zero voltage. Furthermore, DE 195 01 430 A1 describes a circuit arrangement for driving an electric motor (1) with the aid of an electronic control system (5) and an electronic circuit-breaker (4), in the case of which the electronic circuit-breaker (5) is switched by the electronic control system (5) in such a way that variable pulses (11, 11xe2x80x2, 20) of an electric voltage (U) can be applied via the electronic circuit-breaker (4) to the electric motor (1) for the purpose of operating the electric motor at a preset speed (n1, n2). The jerky or impulsive movement of the rotor of the electric motor (1) is achieved here by virtue of the fact that the electronic control system (5) includes means for disconnecting the electronic circuit-breaker (4) during at least parts of at least individual pulses (11, 11xe2x80x2, 20).
The disadvantage of driving an electric motor in such a way consists in that in the case of a phase-gating controller, for example, a constant number of half waves of an AC voltage are respectively completely cut out. This measure is disruptive, particularly in the case of a low speed, that is to say in the case of large gating of the remaining half waves, since a continuous speed is more advantageous during a screwing operation in the case of a low speed.
EP 0 784 884 B1 discloses an electronic system with the aid of which it is also possible to set a jerky speed. Here, an electric screwdriver is described which has a universal motor (1) which is driven by means of a phase-gating controller (3) for determining variable speeds, it being possible for the phase-gating controller (3) to be switched over to wave-packet-controlled phase-gating control. It is also the case that not all half waves of the system are passed in the case of wave-packet-controlled phase-gating control. The passing and non-passing of the half waves is achieved with the aid of an oscillator (4) which can be connected to the phase-gating controller. The further the frequency of the oscillator (4) is situated below the system frequency of 50 Hz, the fewer half waves of the system are passed.
The mode of operation of this controller corresponds to that of DE 195 01 430 A1, and the disadvantage is therefore also the same.
Laid-Open Patent Application DE 196 09 986 A1 describes a method for operating an electric motor in the case of which use is made of an electronic system with the aid of which it is possible to achieve a first, a second and a third speed. In the case of AC operation of the electric motor, the electronic system comprises a phase-gating controller, and the electric motor is used with electric screwdrivers. The first preset speed is used to turn in the screw until the screw head comes into the vicinity of the material surface, the first operating phase. Once the previously set limiting torque is achieved, the electronic system of the electronic motor is switched over into a further operating phase, and the motor is now driven in such a way that a periodically interrupted so-called secondary torque of the electric motor is exercised by means of torque pauses of a specific length. In the second operating phase, the electronic switch is periodically reconnected, it being possible for the pauses in the reconnection to be up to one second, column 7, line 5 to 10. On the one hand, this is a question of a method in which phase-gating control can be switched over to wave-packet control, column 5, lines 30 to 51, in a fashion similar to the method from EP 0 784 884 B1. On the other hand, it is disclosed in this document that the second speed corresponds to a minimum current flow angle, column 6, lines 53 to 56, column 7, lines 52 to 56. It emerges from the description and the drawing in this document that the electronic system of the phase-gating controller effects at least two or three operating states in an electric tool, the first and the second or the third operating states being a function of the level of the power consumption of the electric motor. If the previously set threshold of the power consumption is exceeded, the electronic system switches over from the first operating state, in which the electric motor of the electric tool can be operated at variable settable continuous steady speeds, into the second and third operating states, in which the electric motor has a more or less jerky rotational behavior.
The method according to DE 196 09 986 A1 with the up to three operating states during a screwing operation with the aid of an electric tool has the disadvantage that the transition from a continuous, steady rotational behavior of the electric motor to a jerky rotational behavior is not performed smoothly, but abruptly.
DE 35 34 052 A1 describes a method for raising an alarm in the event of overloading in the operation of an electric tool, which gives the user an unambiguous indication, which cannot be overlooked, of the overload state. In the event of an overload state, the described method effects a lowering of the power fed to the electric tool, as a result of which the speed of the electric motor is reduced, and subsequently cyclical raising and lowering of the reduced fed power is additionally performed, as a result of which the speed of the electric motor swings to and fro in the case of lowered power until the overload state is terminated. The electric tool is assigned a phase-gating controller controlled by a microcontroller for the purpose of speed control.
The method described here is not applied to screwing and drilling operations with the aid of an electric tool, since lowering the reduced fed power, which is swinging to and fro, is unsuitable for such applications.
It is the object of the invention to create a controller for a commutator motor which delivers a smooth soft transition from a steady rotational behavior of the motor to a jerky rotational behavior of the motor which in the case of a continually rising torque is proportionally amplified accordingly.
This object is achieved by means of the distinguishing features of the independent patent claims 1, 5, 7. Advantageous features of the configuration of the invention are to be gathered from the remaining claims and the description.
The advantage of the controller according to the invention for a commutator motor resides in the fact that the phase-gating controller is assigned control devices with the aid of which a first gating of the half waves of an AC voltage into first subranges, and a second gating of the half waves into second subranges can be carried out to the effect that in the case of a low speed and a low torque a steady rotational behavior of the motor is achieved, and in the case of a continuously rising torque a soft transition, proportional to the torque, is achieved to a jerky, self-amplifying rotational behavior of the motor, such a rotational behavior of the motor advantageously occurring without transitions.
This rotational behavior of the motor is particularly advantageous in the case of screwing operations with the aid of an electric tool. A pulse-width modulator is applied analogously in the case of DC operation of the commutator motor.